The major part of this paper was written when P.T. visited the Meudon Observatory in October 1997. He thanks Lucette Bottinelli, Lucienne Gouguenheim and Gilles Theureau for their hospitality during the visit. This work has been supported by the Academy of Finland (project "Cosmology in the local galaxy Universe"). We thank the referee for useful criticism which helped us to clarify the presentation. We are also grateful to Chris Flynn for helpful comments on the manuscript.
© European Southern Observatory (ESO) 1999
Online publication: March 1, 1999